1. Field of the Invention
This invention relates, in a general manner, to a quality checking of digital channels carrying plesiochronous digital signals through a multiplex digital link having, at its input, a multiplexing equipment synchronizing the plesiochronous signals by stuffing and time-division multiplexing them into a resultant signal and, at its output, a demultiplexing equipment performing the reciprocal operations to the above. Quality checking is aimed particularly at monitoring the channels, to generate alarms, and to locate operation faults in circuits included in the equipments.
2. Description of the Prior Art
Cyclic monitoring equipment for checking the operation of a multiplexing or demultiplexing equipment is known. As described in paragraph 3 of the article by PORTEJOIE et al., entitled "EQUIPEMENT DE MULTIPLEXAGE NUMERIQUE TNM 2-4 ET EQUIPEMENTS DE SURVEILLANCE ASSOCIES" (TNM 2-4 DIGITAL MULTIPLEXING EQUIPMENT AND ASSOCIATED MONOTORING EQUIPMENT), published in CABLES & TRANSMISSION, N.sup.0. 2, April 1978, pages 246 to 277, a monotoring equipment associated with a multiplexing equipment, or a demultiplexing equipment, cyclically compares incoming plesiochronous signals to be multiplexed into an outgoing resultant signal, or outgoing plesiochronous signals obtained by demultiplexing an incoming resultant signal, with second plesiochronous signals obtained by demultiplexing the outgoing resultant signal, or incoming resultant signal, in an auxiliary demultiplexing equipment. These bit by bit comparisons provide a check to assure that the data relating to a component plesiochronous signal is not degraded during transcoding, synchronizing-stuffing and multiplexing operations, or desynchronizing-unstuffing, demultiplexing, and transcoding operations, to which the component signal is subjected in the equipment.
However, bit by bit comparisons between two similar component signals, one incoming or outgoing, the other regenerated by auxiliary demultiplexing equipment, necessitates the use of complex and costly circuits. Furthermore, auxiliary demultiplexing equipment of this type is necessary at each end of a digital multiplex link.